coordinateconversions: Convert to and from row and colum indices, and x and y...

In ethanplunkett/gridprocess: Package for processing raster data

Convert to and from row and colum indices, and x and y coordinates

Description

x2c and y2r return the integer column or row of the x or y dimension while the fractional versions return real rows and columns. In most cases the non-fractional version will be prefered.

c2x and r2y return the position along the x or y dimension of the center of the cell as a real number; these do not work with fractional row and column values.

Usage

c2x(c, list, cellsize = list$cellsize, xll = list$xll)
r2y(r, list, cellsize = list$cellsize, yll = list$yll, nrow = list$nrow)
x2c(x, list, cellsize = list$cellsize, xll = list$xll)
y2r(y, list, cellsize = list$cellsize, yll = list$yll, nrow = list$nrow)
x2fractionalc(x, list, cellsize = list$cellsize, xll = list$xll)
y2fractionalr(y, list, cellsize = list$cellsize, yll = list$yll, nrow = list$nrow)

Arguments

r, c	The row and column index of the focal cell.
x, y	x and y coordinates of a point in map units
list	A list describing spatial location and extent of a grid or access window containing the following items: xll, yll, nrow, and cellsize, see arguments with the same names. This can be a grid, the information returned by tiledetails griddescribe, or any other list that contains the appropriate elements.
cellsize	The size of each cell in map units.
xll	The x coordinate of the lower left corner of the lower left (southwest) cell in the landscape or grid.
yll	The y coordinate of the lower left corner of the lower left (southwest) cell in the landscape or grid.
nrow	The number of rows in the landscape or grid

Details

These functions provide two ways of passing the spatial reference information: 1. as a list or 2. explicitly by using the remaining arguments. If both are used the explicit arguments take precedence. Using the list argument is convenient as none of the subsequent arguments are required and generally the information will already be in list format as in a grid object.

Value

x2c and y2r return the column and row index (integer) of the corresponding x and y dimension. r2y and c2x return the y or x dimension (a real number) of the center of the cells with the corresponding row or column index. x2c and y2r return the precise location in column and row space (a real number) of of the corresponding x and y dimension.

Author(s)

Ethan Plunkett

See Also

grid-class

Examples

g <- asgrid(matrix(1:12, 3, 4, byrow = TRUE), xll = 0, yll = 0, cellsize = 10)

x = c(5, 15)
y = c(11, 21)
plot(g, restore.par = FALSE)
points(x, y)
g$m[cbind(y2r(y, g), x2c(x, g))] # sample x and y locations from grid

x2c(20, g)  # x and y values that fall exactly on the boundary are
y2r(10, g)  # considered part of the row or column with the lower index value
            # This is the cell to the west or north
            # as the first row in the matrix is the northernmost and the first
            # column is the westernmost

ethanplunkett/gridprocess documentation built on Feb. 1, 2024, 2:24 a.m.